When a display is exposed to external light such as various illumination, natural light, and the like, an image formed by reflected light inside the display is not clearly focused on the eye to cause deterioration in contrast, and thus there is difficulty in viewing a screen, and eye fatigue and headaches are caused. For this reason, there is also extremely strong demand for anti-reflection.
In a substrate on which a single-layer anti-reflective film is formed, when an index of refraction of the substrate is defined as ns and an index of refraction of the single-layer anti-reflective film is defined as n, a minimum value of reflectance R of the anti-reflective film is represented by (ns−n2)2/(ns+n2)2. Since the minimum value of the reflectance R is obtained when n2=ns is satisfied, the reflectance becomes lower, as the index of refraction n of the single-layer anti-reflective film becomes closer to (ns)1/2. Generally, considering an index of refraction ns of polyethylene terephthalate used as a substrate in transparent conductive films is about 1.54, it is desirable that the index of refraction n of the anti-reflective film be closer to a range from about 1.22 to about 1.24 as far as possible to reduce the reflectance R thereof.
Typically, the anti-reflective film includes an anti-reflective layer formed on a light transmitting base. For example, Japanese Patent Laid-open Publication No. 2002-200690 discloses an anti-reflective layer having a three-layer structure in which a hard coating layer, a 1 μm or less thick high index of refraction layer and a low index of refraction layer are stacked in order from a light transmitting base.
In addition, to simplify a manufacture process, Japanese Patent Laid-open Publication No. 2000-233467 discloses a two-layer structure in which a hard coating layer and a low index of refraction layer are stacked without a high index of refraction layer in the aforementioned anti-reflective film.
Due to development of hollow silica particles which have a low index of refraction, low index of refraction coating materials having an extremely low index of refraction have been studied. However, an index of refraction of the low index of refraction coating materials developed using an existing acrylic resin has not reached 1.22 to 1.24 corresponding to the theoretically optimum value for anti-reflection. Although various attempts have been made to solve this problem by addition of a fluorine-containing polymeric material to reduce an index of refraction, there is a problem of increase in surface energy of a coating surface. In addition, due to poor compatibility of the hollow silica particles with the acrylic resin, it is necessary to perform surface treatment of the silica particles allowing the silica particles to be bonded to the acrylic resin.
Korean Patent Laid-open Publication No. 2004-0070225 discloses a coating composition including a silica precursor obtained by hydrolysis and polycondensation of an alkoxysilane. However, since a method of condensation and thermal curing of a silane compound provides insufficient curing upon low-temperature and short-time thermal curing and thus requires high-temperature or long-time curing for sufficient curing density, the method has a number of problems such as increase in production cost, deterioration in productivity, damage to a plastic film base, crack generation in a hard coating layer due to shrinkage caused by heating, and the like.
In addition, although a technique for manufacturing a low index of refraction coating layer by introduction of a fluorine-containing alkoxysilane can also be suggested, there is a limit in application of the technique since there are problems such as phase separation and the like.
Therefore, there is a continuous need for development of a method in which a silica coating layer having a low index of refraction can be formed on a base without phase separation.